I think lowering the voting age is a good thing, but I think it misses the symptom for the cause. Younger people aren't voting for a reason, and lowering the voting age to 16 encourages that habit at the heart. That's very important. We know that once people vote, they continue to vote, so that certainly would have a beneficial effect.
The other two things I would mention are things that have just been mentioned: increased civics education and empowering organizations like Student Vote, which does civics education in high schools at the grassroots level, to facilitate and encourage that conversation about youth engagement.